J. KalinowskiInvisible sneutrino Pinning down the invisible sneutrino at the ILC Jan Kalinowski U Warsaw

J. KalinowskiInvisible sneutrino Outline  Motivation  The setup  Signal and background processes  Imposing cuts  Results  Summary and outlook In collaboration with W. Kilian, J. Reuter, T. Robens, K. Rolbiecki, JHEP10(2008)090

J. KalinowskiInvisible sneutrino Standard way of determining sneutrino mass  select with subsequent  primary lepton energy spectra => sneutrino and chargino mass  di-jet invariant mass spectrum => mass difference  for tau-sneutrino more problematic due to t decay Motivation Martyn ‘03 already exploited by Freitas, Porod Zerwas ‘05  dominant decay  invisible decay products  can nevertheless ‘see’ sneutrino in the inverse process In some scenarios, e.g. SPS1a’

J. KalinowskiInvisible sneutrino Setup What’s new???  Revisit the analysis using full matrix element for both signal and background include all interference and off-shell effects get a handle on multi-particle final states (up to 10 particles) include all SUSY and SM reducible and irreducible background  Tools: Monte Carlo event generator WHIZARD (Kilian, Ohl, Reuter) matrix element generator O’Mega (Moretti, Ohl, Reuter) so far LO MC for production+ decay implemented  Environment e+e- at E CM = 500 GeV bremss- and beamstrahlung automatically included

J. KalinowskiInvisible sneutrino Working scenario: SPS1a’ mSUGRA point:

J. KalinowskiInvisible sneutrino Signal Chargino pair production with subsequent leptonic decay o BR( ) = 13% o sneutrino decays invisibly o final state: two opposite-charge leptons + missing energy o select leptons of different flavor Proper signal

J. KalinowskiInvisible sneutrino Irreducible SUSY processes like  chargino decays to W+neutralino  single-resonant diagrams  non-resonant diagrams  slepton-pair production  SM decaying to SUSY, …. Proper: 3.06 fb (2.50 fb with -strahlung) 6-fermion: 4.69 fb (3.94 fb with -strahlung) Signal: proper + irreducible SUSY

J. KalinowskiInvisible sneutrino SUSY background  SUSY: different sources - here according to # t’s Compare to Preselection: 5 0 cut for the final electron 1 0 cut for particles vanishing in the beam pipe Signal / SUSY Bkgd ~ 1 / 3

J. KalinowskiInvisible sneutrino SM background  WW, single W, tau pairs  Photon induced: tau pairs, charm pairs, … Signal / Bkgd ~ 1 / 10 5

J. KalinowskiInvisible sneutrino Event selection  Many different background processes with different kinematics  Dominant: photon-induced tau-pair: low p T, back-to-back Example: p T and Df of signal and tt background

J. KalinowskiInvisible sneutrino Suppressing the background Set of cuts: After the cuts: SM almost disappears, SUSY still substantial

J. KalinowskiInvisible sneutrino Determining the sneutrino mass: 1  The dependence on the sneutrino mass enters  in the production (t-channel exchange)  in the decay For the SPS1a’ point strong dependence since close in mass

J. KalinowskiInvisible sneutrino Determining the sneutrino mass: 2 a)no beam- and bremsstrahlung b)on-shell kinematics Assuming the lepton energy spectrum flat between endpoints E min, E max However, spectrum distorted because of  chargino polarization effects  beam- and bremsstrahlung  off-shell and interference effects  SUSY background, in particular t  SM background  response of signal to selection cuts

J. KalinowskiInvisible sneutrino Effect of cuts e m before after cuts blue – proper signal green – irred. SUSY

J. KalinowskiInvisible sneutrino Determining the sneutrino mass: 2 e m signal SUSY bg. SM bg. Lower edge difficult to identify Assuming chargino mass known

J. KalinowskiInvisible sneutrino Determining the sneutrino mass: 3 Binned ch 2 fit: generate MC control samples for varying sneutrino mass nominal

J. KalinowskiInvisible sneutrino Summary  ”Invisible” sneutrino becomes visible in leptonic decays of charginos  our analysis included  full matrix element for 2 -> n processes (n b 10)  off-shell and interference  all SUSY and SM background, including gamma-induced  mass measurement possible but not easy  three methods for sneutrino mass from leptonic decays of charginos  production cross section – good control of normalisation necessary  lepton energy spectra – strong effect of kinematic cuts  chi2 fit to templates with varying sneutrino mass Outlook: NLO production implemented into WHIZARD ( Kilian, Reuter, Robens) NLO decays calculated (Rolbiecki, Fujimoto ea) Full NLO MC analysis feasible in future

J. KalinowskiInvisible sneutrino

J. KalinowskiInvisible sneutrino Proper vs irred. SUSY, 800 GeV e e m m m m all cuts energy+ angle cuts energy+angle+p T cuts signal SUSY bg.

J. KalinowskiInvisible sneutrino Ecm=800 GeV signal all m m m all cuts e